DC electric arc furnaces currently carry the arcing power to the arc via a melt or hearth electrode or connection, through the charge, the arc, and so to the arcing electrode.
The hearth or melt electrode forms electric connection with the melt in the furnace via a metal bar having an inner end open to the melt and melted by the melt, the electrode projecting through the hearth or an adjacent portion of the hearth and into the melt, the outer unmelted end forming an electrical connection. The construction is such that an electrical connection of adequate current-carrying ability cannot be established via a metal scrap charge; electrical connection can only be established adequately via a melt in the furnace and in contact with the melt or hearth electrode.
Therefore, when a DC arc furnace is being started up, having just been charged with a pile of scrap, it has heretofore been necessary to use a starting electrode which is temporarily pressed against the scrap pieces under adequate pressure to provide an electrical connection having enough current-carrying ability to supply the arc which by its heat initiates melting of the scrap pieces. This starting electrode has, according to the prior art, been thrust against the scrap diagonally via openings in the furnace side wall, or has been inserted through the furnace roof, in both instances requiring special openings through the usual furnace construction and which must be sealed more or less gas-tightly, while, of course, requiring suitable electrode moving equipment in the form of hydraulically operating reciprocating devices and the like. It has been necessary to temporarily thrust the starting electrode against the initial charge of scrap so as to form a firm electrical contact with the scrap, and after melting has proceeded enough to form a pool of melt contact the melt electrode or connection built somewheres into the hearth, so that this connection becomes operative, to withdraw the starting electrode with the melt-down then proceeding to completion. The Andersson and Stenkvist U.S. Pat. No. 4,081,974 discloses one way to use a starting electrode without requiring special openings through the furnace vessel or its roof and to thereby eliminate the requirement for sealed openings for accommodating the starting electrode. However, this patented arrangement still requires the use of manipulating devices. The disclosure of this patent is hereby made a part of the present disclosure.